1. Field of the Invention
The present invention is directed to a tubing hanger assembly. More particularly, the present invention is directed to a tubing hanger seal assembly which provides a peripheral seal between the tubing hanger and the housing of a subsea wellhead. The tubing hanger seal assembly of the present invention has a Z-pack seal which is set upon running the tubing hanger assembly into the subsea wellhead. The tubing hanger seal assembly can be separately removed from the tubing hanger.
The tubing hanger assembly of the present invention is especially suited to be utilized in conjunction with subsea wellhead systems which have multiple casing strings and sealing casing hangers as disclosed more particularly, for example, in U.S. Pat. No. 4,488,740, which is incorporated in its entirety herein by reference. U.S. Pat. No. 4,488,740 discloses a subsea wellhead system which has multiple concentric casings. For example, the casings can range from sixteen inches down to seven inches. The tubing hanger assembly of the present invention is adapted to be seated above the uppermost casing hanger in the subsea wellhead system.
Another aspect of the present invention is that a running tool is specially designed to run the tubing hanger assembly of the present invention into position in the subsea wellhead an set the seals of the seal assembly in a single trip. The running tool is adapted for testing the seating of the tubing hanger and the tubing hanger seal assembly associated therewith in the subsea wellhead and for testing the seals between the tubing hanger and the subsea wellhead housing and between the tubing hanger and the casing hanger on which it seats to make certain that the seals can withstand the expected operating pressures.
2. Prior Art
U.S. Pat. No. 4,561,499 discloses a tubing suspension system for undersea well production operations which employs a non-oriented tubing hanger having an inner body for supporting a tubing string and a landing collar for supporting the tubing hanger on a wellhead casing. The tubing hanger includes three cooperating concentric sleeve assemblies which are employed to lock and seal the tubing hanger to the wellhead housing. The outer sleeve assembly includes a locking actuator and a dual seal assembly and is separately retrievable from the remainder of the hanger assembly. A non-orienting hydraulic set running tool is employed to run the tubing hanger, set the seals, lock the tubing hanger to the wellhead casing, and retrieve either the outer sleeve assembly or the entire tubing hanger. The running tool includes a hydraulically controlled actuating sleeve which carries a latch dog assembly which locks with the tubing hanger.
U.S. Pat. No. 4,381,868 discloses a pressure-actuated wellhead sealing assembly. The seal assembly is for sealing across an annular recess between the interior of a wellhead member and the exterior of a tubular member. The seal assembly includes a heat-resistant seal ring in the annular recess, a pressure-responsive ring for moving the seal ring into sealing position in the recess, latching means to retain the pressure-responsive ring in set position and spring means between the seal ring and the pressure-responsive ring to maintain a sealing force on the seal ring.
U.S. Pat. No. 3,809,158 discloses a well completion apparatus and method. The well completion apparatus includes a casing hanger which is suspended from a first member of a well tool and a sealing member which is suspended from a second member of the well tool. The first and second members are releasably connected whereby, upon landing the casing hanger within the well, the first member is disconnected from the second member and the sealing member is lowered into sealing position independently of the casing hanger. A portion of the sealing member is rotated to cause an expansion ring to engage an annular groove in the casing head thereby actuating the sealing member and locking the sealing member and casing hanger in position.